OFDM (Orthogonal Frequency Division Multiplexing) is attracting attention as a high-speed transmission technology resistant to multipath interference. FH-OFDM (Frequency hopping-OFDM) is a scheme whereby OFDM subcarriers that are used hop around, over time, and is used in, for example, IEEE802.16, as an access scheme that is capable of achieving frequency diversity effect (see, for example, “IEEE Standard 802.16: A technical overview of the Wireless MAN Air Interface for broadband wireless access”, pp. 98-107, IEEE Communication Magazine, June, 2002).
Furthermore, FH-OFDM also has an effect of averaging interference between cells in a cellular environment and is drawing attention as a future high-speed radio transmission technology. Furthermore, the 3GPP is also studying the introduction of FH-OFDM.
In FH-OFDM, base station apparatuses carry out transmission according to their respective FH patterns. An FH pattern is a pattern related to time transition and an operating frequency (subcarrier) and each base station apparatus is assigned a unique FH pattern. The frequency of FH (frequency hopping) may be once every symbol or every slot (or frame). Here, suppose FH for every symbol. Because a frequency is used over a wide range, effects of FH include a frequency diversity effect and a temporal averaging effect against interference between cells.
As a method for implementing FH, for example, a method of using frequency interleave and a method of using a pattern generated by a random sequence such as a PN sequence may be available. For simplicity, the latter will be explained here.
Furthermore, for the purpose of channel allocation per cell, there is a proposal to divide a band into subchannels and carry out DCA (Dynamic Channel Allocation) in subchannel units (e.g., see “Dynamic channel allocation schemes in mobile radio systems with frequency hopping”, Verdone, R.; Zanella, A.; Zuliani, L., pp. E-157-E-162, vol. 2, Personal, Indoor and Mobile Radio Communications, 2001 12th IEEE International Symposium on, September/October 2001).
A conventional base station apparatus and mobile station apparatus will be explained below. FIG. 1 is a block diagram showing the configuration of a conventional base station apparatus.
In FIG. 1, a scheduler section 11 carries out scheduling using CQI (Channel Quality Indicator) from each mobile station apparatus to determine to which user data should be sent. There are various scheduling algorithms such as an MaxC/I method and Round Robin method. Furthermore, a coding method (coding rate) and modulation scheme to be used are determined based on this CQI. A coding section 12 carries out coding such as turbo coding on user data. Furthermore, the coding section 12 also carries out processing like interleaving as required.
A transmission HARQ section 13 carries out processing necessary for HARQ. Details will be explained using FIG. 2. FIG. 2 is a block diagram showing the configuration of a transmission HARQ section of the conventional base station apparatus. As shown in FIG. 2, the transmission HARQ section 13 is constructed of a buffer 21 and a rate matching section 22. The buffer 21 stores a bit string of transmission data. The rate matching section 22 carries out rate matching determined by an RM parameter on the bit string of the transmission data and inputs punctured or repeated transmission data to a modulation section 14. The RM parameter may vary depending on a transmission count.
The modulation section 14 modulates the transmission data according to QPSK or QAM. A control data processing section 15 is constructed of a coding section 16 and a modulation section 17. The coding section 16 carries out coding on control data. The modulation section 17 modulates the control data. A multiplexing section 18 multiplexes (here, time multiplexing) the transmission data subjected to processing by the modulation section 14 with the control signal which has been likewise subjected to processing of coding and modulation.
Next, a subcarrier mapping section 19 assigns the transmission data and control signal to subcarriers according to a predetermined FH pattern. Likewise, the subcarrier mapping section 19 also maps pilot signals in such a way as to be distributed over the entire frequency band. Then, the subcarrier mapping section 19 outputs a transmission signal to which the transmission data, control signal and pilot signals are mapped to an S/P conversion section 20.
The S/P conversion section 20 converts the transmission signal from serial data to parallel data and outputs the parallel data to an IFFT section 21.
The IFFT section 21 carries out an IFFT (inverse fast Fourier transform) on the transmission signal which has been converted to the parallel data. A GI insertion section 22 inserts a GI (Guard Interval) into a transmission signal to enhance multipath resistance. A radio processing section 23 transmits the transmission signal after radio transmission processing.
The state of subcarriers used at this time is as shown in FIG. 3, for example. FIG. 3 illustrates an example of signals of the conventional base station apparatus. In FIG. 3, the vertical axis shows time and the horizontal axis shows subcarrier frequencies. As shown in FIG. 3, subcarriers carrying pilot signals and data signals vary every time unit.
In this way, a mobile station apparatus receives signals carried by time-varying subcarriers on which transmission signals are arranged. FIG. 4 is a block diagram showing the configuration of a conventional mobile station apparatus.
In FIG. 4, a radio processing section 51 carries out radio reception processing such as down-conversion on a received signal and obtains a baseband signal. A GI elimination section 52 eliminates the inserted GI. An FFT section 53 carries out FFT processing and thereby extracts the signals of the respective subcarriers. A subcarrier demapping section 54 demaps this received signal according to an FH pattern and extracts the signal assigned to the own station.
Next, a channel separation section 55 separates the received signal into a user signal, control signal and pilot. A demodulation section 56 demodulates the control signal and a decoding section 57 carries out decoding processing on the control signal subjected to the demodulation processing.
A demodulation section 58 demodulates the user signal. A reception HARQ section 59 saves a predetermined number of bits (here, soft decision bits) after the demodulation of the user signal. In the case of retransmission, the bits are combined with the reception bits previously stored. A decoding section 60 carries out decoding on turbo codes, etc., using the bit string to obtain user data. Here, though not shown, a channel estimation value calculated using pilot signals is used during demodulation processing. An ACK/NACK generation section 61 decides based on a CRC result of the decoded received data whether the received data includes errors or not and transmits an ACK signal or NACK signal over an uplink.
Furthermore, a CIR measuring section 62 calculates an average reception SIR of all subcarriers using pilot signals. A CQI generation section 63 generates CQI from the average reception SIR. A transmission section 64 transmits the CQI and ACK/NACK signal over the uplink.
However, while the conventional apparatus can achieve a frequency diversity effect by expanding a band used through frequency hopping, there is a problem that it cannot obtain effects of frequency scheduling whereby transmission is performed using frequencies in a good propagation path situation. Furthermore, since the frequency hopping range of the conventional apparatus extends over a wide band, an amount of control information becomes enormous when hopping patterns are assigned to the respective users as channel resources.
Furthermore, according to conventional frequency scheduling whereby packets are transmitted using frequencies of good reception quality, when a base station apparatus in an adjacent cell also assigns the same frequency to other mobile station apparatuses, it may not be possible to receive packets due to interference.